FIG. 7 is an exploded view of one-way clutch 300 from commonly owned U.S. patent application Ser. No. 12/316,219, filed Dec. 10, 2008. Clutch 300 includes inner race 302, wedge plate 304, and outer race 306. Race 302 is fixed against rotation via splines 308. When the outer race rotates in circumferential direction CD1, clutch 300 is in free wheel mode, the outer race rotates with respect to the inner race and the wedge plates, and the entire inner circumference 310 of the outer race is in frictional engagement with the outer circumference 312 of the wedge plate. When the outer race reverses direction to rotate in circumferential direction CD2 (locking mode), the wedge plates expand against the inner and outer races to lock rotation of the outer race to rotation of the inner race, that is, to rotationally fix the outer race.
Some frictional engagement of the wedge plate and outer race is necessary to enable the clutch to shift from free wheel mode to locking mode; however, the frictional engagement also opposes rotation of the outer race, which dissipates a torque load applied the outer race. Thus, the frictional engagement decreases the efficiency of a device using clutch 300. In clutch 300 the frictional engagement and attendant decrease in efficiency is maximized due to the full contact of circumferences 310 and 312.
U.S. Pat. No. 3,202,250 discloses a one-way clutch with an inner race, one or more wedges, and an outer race. As described above, the full extent of the respective outer circumferences of the wedges are engaged with the inner circumference of the outer race, resulting in the maximization of the frictional inefficiencies described above.